The multiplexes are jammed with movies for children, but how many great films about childhood are there? Francois Truffaut (“The 400 Blows,” “Small Change”) knew the terrain and 2011’s “Monsieur Lazhar” got wrenchingly under the skin of its Montreal grade-schoolers. Mostly, though, the movies are content to show our kids things without ever being curious about how they see things.

“What Maisie Knew,” a modern-dress adaptation of the 1897 Henry James novel, reverses the trend: It’s told entirely from the point of view of a 6-year-old girl as she watches her parents’ relationship come apart. Maisie (the remarkable Onata Aprile) is adorable without being a Cute Kid, and while she occasionally seems too placid — would one tantrum have been too much? — her watchfulness is the point. As in the novel, Maisie is witness to the foolishness of people who call themselves grown-ups. What she gradually comes to understand is that she is their victim as well.

The setting is New York’s SoHo, which the gifted directing team of Scott McGehee and David Siegel (“The Deep End,” “Bee Season”) paint as an enchanted forest of sunlight and sidewalks. Here be monsters, even if Maisie doesn’t know it: her mother, Susanna (Julianne Moore), a neurotic alt-rock superstar edging past her prime, and her father, Beale (Steve Coogan), a well-spoken British art dealer with the gift of shirking responsibility.

Honestly, can you imagine two worse parents than Moore and Coogan, or at least the characters these actors tend to play? “What Maisie Knew” practically opens in mid-diatribe, Beale yelling “I’ve done my midlife crisis, why don’t you get on with yours?” as Susanna breaks things and Maisie plays in the other room, the words cruising somewhere in the ether above her head. She’s heard all this before.

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After a brief custody battle experienced by the little girl as tedium, questions, and hard courthouse benches, Maisie gets shuttled between her father’s and mother’s apartments. The former is full of new toys that aren’t yet hers and her much-loved nanny, Margo (Joanna Vanderham), who has naively taken up with Beale. In a foolish bid to establish her own parenting bona fides, Susanna retaliates by marrying the lanky, footloose Lincoln (Alexander Skarsgård). “He’s pretty much a bartender,” she tells her daughter. “I married him for you.”

James was chronicling and criticizing the selfishness of Gilded Age British society, and screenwriters Nancy Doyne and Carroll Cartwright don’t have to stretch to fit their tale to 21st-century Manhattan. “My daddy married my nanny, so the court made my mommy marry Lincoln” is how Maisie benignly explains it to her classmates, and none of the teachers bat an eye.

“What Maisie Knew” is about the erosion of innocence in the midst of plenty, and if it doesn’t follow the title character into adolescence, as James did, it catalogs the many insults, small and large, against Maisie’s faith in the adult world. Yet the film rarely feels heavy-handed, so serene is its own faith in its heroine’s strength.

Maisie gets passed around from person to person — as if she’s a casserole dish — and we gradually come to see that Margo and Lincoln have the innate gift of kindness the girl’s parents lack. Maybe it’s because they’re younger and poorer, or maybe because those who get used by users form natural bonds of empathy. When Lincoln takes Maisie for a frolic on the High Line (the latest go-to New York location), you breathe a sigh of relief. And you wonder, as the filmmakers do, why terrible parents can’t simply be fired. It’s an irresistible fantasy, one that James and this film explore in different ways.

Moore’s Susanna is an easy character to hate, and you’re happy to do so for much of the running time. The role’s grating in a way we’ve come to expect from this actress — unlikability sometimes seems a point of pride with Moore — but she lets us see the helplessness, too. Susanna’s desperate to be a good mother but she’s more terrified of becoming a square. Toward the end she gets the kind of moment that life rarely offers but the movies, falsely but thankfully, do, where self-awareness comes flooding into her face and she almost crumples with the knowledge of what she has done to her child.

That moment, again, passes over Maisie’s head, even as the girl takes her first gentle step toward becoming her own person. The film ultimately belongs to its lead actress, and Aprile gives a performance that’s not really a performance at all. She’s merely present in her dreamy actuality, preoccupied by the foreground (as kids are), absorbing and translating adult events (as kids do), and pulling her head in as necessary, like the turtles that occur throughout the film as a visual motif. “What Maisie Knew” flirts with sentimentality but mostly keeps it at bay until the very end, at which point the filmmakers and we realize the kid has probably earned it. Turtles survive. So will Maisie.